A valve control known from DE-OS 36 34 728 provides that the flows of volume (volume flows), which are determined by the opening cross section of the control valves, are maintained constant with the same ratio even through individual simultaneously operating users have different loads. This is achieved by arranging downstream of a metering orifice of each control valve a pressure compensator ((throttle valve). The control spool of said pressure compensator is subjected to the pump pressure in the direction of the opening, and to the highest load pressure occurring in one of the users in the direction of closing. Thus, the pressure pressure compensator will control the volume flow of the pressure medium such that the pressure differential occurring at the control valve will remain constant even if different load pressures exist. Consequently, also the appropriate flow of the pressure medium (working liquid) and the operating speed, respectively, of the user remains constant. In said known hydraulic system, a plurality of user is supplied by a single controllable or variable pump via a respective control valve and a respective pressure compensator. Further, in said system, the highest pressure occurring at one of said users is selected by means of a chain of shuttle valves and is guided to all pressure compensators to act in the closing direction. Thus, the control spools of the pressure compensators will adjust such that at the respective metering orifices in the control valve, always the same pressure differential exists, even for different loads of the users. This is basically a valve control for dividing the pump flow into individual partial flows flowing to each user, wherein even for different loads of the users, the ratio of the divisional flows remains constant and thus, the desired speed is maintained. This ratio of the divisional flows remains constant even if the source of pressure medium does not supply enough volume flow for supplying all users. In such a situation, all partial flows will be reduced, however, the ratio amongst the partial flows remains constant. Inasmuch as the control conduits are relieved towards the tank in the center position (zero position), the known valve controls show a short time pressure reduction in the user conduits when starting and if a change of direction occurs, respectively. This is so, because the amount of pressure medium (control oil) for the load sensing conduit has to be replenished from the user ports. Said pressure reduction has the consequence that the users under load will sink for a short time.
For another type of valve control (DE-OS 36 05 312) it is already known to avoid said sinking of the load. For this purpose, two additional auxiliary spools are provided in the main control spool with respective switching spools. This solution is very costly and can be used only up to a certain nominal valve size.
The present invention is directed to overcoming one or more of the problems of the prior art.
It is an object of the invention is to provide a valve control arrangement which will avoid the occurrence of a sinking of the load during a control operation independently of the size of the valves.
It is another object of the invention to provide a load independent valve control using relatively simple and less costly hardware.